The United States and Japan will step up their defence cooperation to deal with the threat from nuclear-armed North Korea as tensions in East Asia remain high, officials from the two allies said on Thursday.

Anti-war protesters block Vic defence base

Anti-war protesters in Victoria have begun a four-day blockade of the Swan Island Military Base as they urge the federal government to avoid war in the Middle East.

Around two dozen protesters gathered at the gate of the base near Queenscliff on Tuesday morning. They will remain there for the rest of the week.

In its fifth straight year of protests, the Swan Island Peace group bears signs calling on the Abbott government to "End the US Alliance" and withdraw Australia's special armed services (SAS) troops from Afghanistan.

The protests come in the wake of the government's support of the US plan to bomb ISIS strongholds.

Group spokesman Greg Rolles says waging all-out war on ISIS is an unnecessary response to recent terror threats.

"Western military intervention has killed hundreds of thousands of people in the last fifteen years," he said.

"The west has given these extremist groups a message of retribution to sell.

The group says it is targeting the base because it believes it is a key facility contributing to the US war on terror. It is home to an SAS unit and also houses Australian Secret Intelligence Service (ASIS) staff.

The group said it is also monitoring the wharves to stop military staff entering the base via the water.

Base staff did not attempt to access the island on Tuesday morning, the group said.